This invention relates to a device for detecting faulty combustion in a controlled-ignition internal combustion engine.
Because of recently passed regulations setting standards of purity for the combustion gases from internal combustion or heat engines, it has become necessary to use purifying devices for processing the exhaust gases. These devices are expensive and are very easily damaged in the event of faulty operation of the engine, since an increase in the content of gases to be eliminated results in an excessive increase in the temperature of the reacting means used in the purifying devices, which consequently melt and are destroyed.
Prior art protection devices detect the temperature of the means to be protected and operate when the temperature rises abnormally. The devices have two disadvantages. Firstly, the inertia of temperature detectors is an obstacle to effective protection and, secondly, they detect, not faulty operation but one of the results thereof. In principal, therefore, the detection occurs some time after the actual event.
In the case of faulty combustion, the actual event occurs at the combustion chamber. Faults are of the following two types: A failure in the ignition spark or unsuitable richness of the gaseous mixture, resulting in faulty combustion of the mixtures; or an absence of a spark, and consequently of combustion.
The object of the invention, therefore, is to provide a device for detecting the aforementioned faults in combustion, the detection occurring as soon as the faults occur, so that protection can be rapid.
Another object of the invention is to provide exact detection, i.e. means capable of detecting faults having a number of levels of seriousness so that various forms of protection can be used, varying from a change in engine operation (which is performed in a simple manner by the driver so that the vehicle can automatically go to a garage to undergo the necessary repairs without endangering the purifying devices) up to a total shut-down if a fault resulting in rapid destruction is detected, via intermediate methods of purification (such as by-passing, cutting off the supply of air, and so on).
Another object of the invention is to provide a detecting device which is independent of the operating conditions of the engine and provides uniform protection during the entire operating cycle of the vehicle.
Another object of the invention is to provide a simple device which does not require any additional ionization pick-up.
Another object of the invention is to provide a device which does not in any way impair the intrinsic qualities of the ignition device but which on the contrary may increase the performance thereof, by providing information which can be used in a process comprising a feedback such as a regulation of the composition of the gaseous mixtures, etc.
The invention is based on the fact that the combustion of a gaseous mixture results in ionization thereof. This well-known phenomenon is at present used for measurements relating to combustion. When the mixture in the combustion chamber burns, it is strongly ionized and acquires the characteristics of an electric conductor.
The device according to the invention makes use of ionization which occurs in the inter-electrode space in the spark plug, by supplying the spark plug with a current supplied by an auxiliary generator. Accordingly, the presence or absence of the aforementioned current indicates both whether the spark is present and the quality of combustion. A signal corresponding to the current is sampled at the terminals of a resistor connected in the electric circuit of the spark plug, and the signal is conveyed to an electronic processing unit whose output signal can actuate various devices for protecting the purifying means and/or can regulate the combustion process if necessary, by injecting the signal into a feedback loop for regulating the composition of gases fed to the engine.